The technical field of this invention is the topical application of personal care agents and, in particular, methods and compositions for topical application of local analgesics.
The topical use of mild counter-irritants to reduce the discomfort of fatigued muscles and irritated joints is a long-standing practice throughout the world. Some of the most commonly employed counter-irritants, alone or in combination, include menthol, eucalyptol, methyl salicylate and camphor. More recently, both nonsteroidal anti-inflammatory (NSAI) agents and steroidal anti-inflammatory (SAI) agents have come into similar topical use, especially among athletes and individuals suffering from arthritis. The most commonly used NSAIs are derivatives of salicylic acid, such as acetylsalicylic acid (aspirin) and triethanolamine salicylate (TEAS). One of the most effective of the standard counter-irritants, methyl salicylate, owes part of its efficacy to the fact that it is also an NSAI. The most commonly used SAIs include hydrocortisone creams.
Ideal compositions for use as topical analgesics should disperse easily onto the skin and deliver their active ingredients in a way that allows a portion to penetrate the skin rapidly, for prompt relief, while also maintaining an active reservoir on the surface of the skin to provide sustained relief. At the same time, the composition should be formulated to enable neat and easy application with a minimum of mess and discomfort, and with a low potential for staining clothes.
Most topical analgesic preparations are creams or lotions which do not fully satisfy these requirements for convenient, neat, comfortable application, prompt relief, and sustained delivery. There thus exists a need for better topical analgesic preparations offering improvements in convenience and efficacy.